The present invention relates to a motor-driven power booster, and more particularly to a motor-driven power booster suitable for use in an automotive motor-driven power steering system.
There are widely known power boosters including an input shaft, an output shaft, and an electric motor for driving the output shaft dependent on either the torque applied to the input shaft or the angular position of the input shaft. Particularly, those power boosters which are used in automotive power steering systems have a resilient member such as a torsion bar for operatively coupling the input and output shafts to each other. Such power steering systems are however disadvantageous in that any variation in the torque produced by the output shaft tends to be transmitted to the input shaft through the resilient member due to a small torque change arising from the automobile running over rough terrain, a torque change arising from the meshing engagement in a rack and pinion which may be employed for torque transmission from the motor to the linkage, the backlash of a speed reducer that may be used for torque transmission, and machining errors. Furthermore, it would not be easy to change the magnitude of the torque transmitted from the output shaft to the input shaft (reactive torque).